1. Field of the Invention
The present invention generally relates to a relative position detection device capable of detecting a reference position of a first member and a second member that are displaceable relative to each other. More particularly, the present invention relates to a straddle-type vehicle in which a drive device, such as a motor or an engine, is controlled using the relative position detection device.
2. Description of the Related Art
In the motorcycle art, an accelerator grip is rotationally mounted on a handlebar and the accelerator is rotated with respect to the handlebar to open and close a throttle valve of the internal combustion engine. On many motorcycles, an electric relative position detection device is used, in which the rotational movement of the accelerator is detected by a potentiometer and the throttle valve is opened and closed by an actuator based upon the output voltage from the potentiometer.
To reduce the likelihood of a malfunction in the potentiometer resulting in undesired throttle positional control, a separate mechanical switch also is provided that is capable of detecting a completely-closed position of the accelerator so as to close the throttle valve if the accelerator is positioned in the closed position and the throttle valve is not fully closed.
An improved system also has been developed that features a magnetic relative position detection device in which a magnet is disposed in an accelerator and the rotational position of the accelerator is detected via changes in the magnetic flux density. In addition, a further improved system makes use of a Hall Effect sensor.
For example, in JP-A-Hei 7-324637, for the purpose of detecting the rotational position of the accelerator so as to control ignition of the internal combustion engine, a magnet is fixed to an accelerator, two digital Hall Effect sensors are secured to the handle and it is judged whether the accelerator is in the idling range, the middle-speed range or the high speed range. Nevertheless, detection of the amount of rotation of the accelerator necessary to control the opening and closing of the throttle valve still is performed using a potentiometer or the like. Moreover, because the magnet is relatively small, if the accelerator grip is rotated, the gap between the magnet and the Hall Effect sensor grows to such a degree that the magnetic flux density exerted on the Hall Effect sensor become very small. Thus, if a magnetic force is present in the vicinity of the sensor, the outside magnetic force can result in improper operation of the system.
Further, FIG. 2 of JP-A-2002-256904 disclosed a relative position detection device in which a permanent magnet is fixed to an accelerator and two Hall Effect sensor that function in the same manner as each other are fixed to a housing fastened to a handle shaft. In this case, although the details are not clear, an electric signal is output in response to the position of the permanent magnet during rotation of the accelerator using two similarly functioning Hall Effect sensors.
However, since in a relative position detection device using a conventional potentiometer, the potentiometer is larger than an accelerator, the potentiometer is more likely to degrade the aesthetics of the vehicle if the potentiometer is disposed around the accelerator. Therefore, it usually is disposed at a position other than around the accelerator and is connected to the accelerator with a conductive wire or the like, which is likely to increase the number of parts, human-hours required for assembling and the like. In addition, over time, the conductive wire is likely to elongate over time and, therefore, increases the need for maintenance.